1. Field of the Invention
The present invention relates to a device and method for confirming that a wire electrode for a wire cutting discharge machine has penetrated a wire guide section on a wire take-out side.
2. Description of the Prior Art
In order to automatically operate a wire cutting discharge machine, a device which can confirm that a wire electrode delivered from the wire delivering side is certainly penetrated through a wire guide section provided on a wire take-out side. There are various method to penetrate the wire electrode through the wire guide section in the wire cutting discharge machine: e.g.: a method by which the wire electrode is inserted through a preset through-hole in the workpiece secured on a table and thereafter is penetrated through a wire guide section, a method by which the wire electrode is caused to penetrate the workpiece by forming its own hole in the workpiece and thereafter is caused to penetrate the wire guide section; and a method by which a wire electrode is caused to pass by the workpiece and then to penetrate the wire guide section.
In any of these methods, the wire cutting discharge machine runs automatically, and it is necessary to confirm that the wire electrode has actually penetrated the wire guide section on the wire take-out side. Accordingly, as conventional) methods of confirming that the wire electrode has penetrated the wire guide section on the wire take-out side, the following means have been devised.
Specifically, for example, in one such means an electrical contact is provided on each of a wire guide on the wire delivery side which feeds the wire electrode to the workpiece, and a wire guide on the wire take-out side which takes out the part of the wire which has been passed through the workpiece. A low voltage is applied between these contacts, which are then short circuited by the wire electrodes. Detection of the disappearance of the voltage difference confirms that the wire electrode has penetrated the wire guide section on the wire take-out side.
In another method, an actuator for a microswitch is provided in the passage for the wire electrode. The configuration is such that when the wire electrode penetrates the wire guide section on the wire take-out side, and the wire electrode is introduced into the wire take-out section so that tension is activated in the wire electrode, the microswitch is activated; when the time interval that the microswitch is activated continuously is greater than a set time interval, this status is detected, confirming that the wire electrode has penetrated the wire guide section on the wire take-out side.
In a method which detects when the wire electrode has penetrated the wire guide section on the wire take-out side, such as in the former example, in the configuration where an electrical contact is provided on both a wire guide on the wire delivery side and a wire guide on the wire take-out side to ensure that the contact of the wire electrode and the electrical contact has occurred, the electrical contact must be provided in the passage for the wire electrode. This creates the problem that the electrical contact can readily obstruct the passage of the wire electrode. In addition, the contact resistance between the wire electrode and the electrical contact is unstable so that the contact detection is unstable.
In addition, in the other configuration, using the microswitch, the actuator of the microswitch may be separated from the wire electrode by an accident. Further, when the actuator is always touching the wire electrode, it is very susceptible to vibrations in the wire electrode or the like. This produces the drawback of a high rate of damage to the actuator.